Alcohol's effect on fatality risk from a physical insult.

Although alcohol's effect on the risk of being involved in a traffic crash is well known, its influence on the risk of death, given that a crash has occurred, is more uncertain. One study published a few years ago finds that alcohol increases such risk. The present study examines alcohol's effect on fatality risk in a crash using data and methods independent of the previous study, and provides estimates as a function of blood alcohol concentration (BAC). Data for drivers with measured BAC who were fatally injured in a two-car crash were selected from the Fatal Accident Reporting System (FARS). The study uses two sets of fatal crashes. For one, the probability that a BAC = 0 driver was killed is low, so that if alcohol increased fatality risk, this would generate additional fatalities at higher BAC levels. For the other set of crashes, fatality risk was sufficiently close to 100% that other factors had little opportunity to influence it. Dividing the fatalities that can be affected by alcohol by those that cannot measures alcohol's influence on fatality risk, and gives that a driver with BAC = 0.1% is 1.9 +/- 0.2 times as likely as is a BAC = 0 driver to be killed in the same crash. The corresponding ratio for a BAC = 0.25% driver is 3.3 +/- 0.5. While derived using the "laboratory" of traffic, there does not appear to be any obvious reason why the results should not apply to physical trauma in general, so a BAC of 0.1% doubles the risk of death from a given impact, and a BAC of 0.25% triples the risk.